Fuel, aviation fuel for example, is known to become contaminated with microorganisms which are naturally present in air. The microorganisms include bacteria, moulds, protozoa, viruses and yeasts. The problem of fuel contamination in fuel systems is inevitable because fuel systems do not operate in sterile environments and the fuel is routinely exposed to air during its life-cycle. Once such microorganisms are in the fuel, their growth invariably occurs especially in hot and humid environments at any fuel-water interface, typically resulting in large colonies forming on the side walls of the aircraft fuel tanks. These colonies (also referred to as biofilms) if not treated, may block filters and more seriously corrode the storage vessel/system structure via the release of acidic by-products.
Ultra-violet (UV) irradiation is extensively used in water purification systems as a germicidal treatment method. It is used in industrial-scale water supply applications as well as in smaller-scale domestic applications (for example, in swimming pools, ponds and aquaria). It is also used to sterilise work surfaces in for example industrial food processing/packaging applications and air ventilation systems. Ultra-violet irradiation has been shown to inactivate a diverse range of microorganisms and achieves this by means of lethal disruption to the nucleic acid bases (DNA and RNA), thereby rendering the microorganisms unusable.
GB2412319 describes an apparatus for disinfecting air flowing along a duct in an air conditioning or ventilating system. The disinfection is achieved using ultra-violet irradiation.
RU2249610 (see the English-language abstract) concerns a method of controlling microbiological damage. There is no enabling disclosure in RU2249610 of treating fuels predominantly with ultra-violet radiation, and indeed RU2249610 appears to teach against the particular suitability of ultra-violet radiation for the treatment of aviation fuels.
U.S. Pat. No. 3,246,144 describes the inhibition of micro-organism growth in petroleum fuel using ultra-violet irradiation, but it is noted that the present inventors are unaware of any successful implementation of the apparatus disclosed therein.
Note also that the significant problem of microbial contamination of stored hydrocarbon fuels has been discussed in the published literature, see for example C Gaylarde et al. Revista de Microbiologia (1999) 30:01-10 ISSN 0001-3714.